The invention relates to a circuit arrangement for a color image recording and reproduction instrument (video recorder) or a colour television receiver with a phase regulation circuit which includes a phase comparator circuit and a voltage-controlled oscillator, where the phase regulation circuit comprises a first input to receive a color synchronization signal and a second input for receiving a signal derived from the oscillator and an output, the output of the phase comparator circuit being coupled to a control input of the oscillator and the oscillator output being coupled to the second input of the phase comparator circuit.
Such a circuit arrangement is known from the book by Limann/Pelka, "Fernsehtechnik ohne Ballast" ("Television technology without a ballast"), Franzis-Verlag, Munich, 14th edition, 1983, pp. 332 to 342, especially FIG. 16.11, with reference to television receivers. The output signal of the voltage-controlled oscillator required for the synchronous demodulation of the square amplitude modulated color difference signals is synchronized with the color synchronization signal in the phase regulation circuit. In PAL systems, the phase of the color synchronization signal alters by 90.degree. from line so that to line the control signal of the phase comparator circuit also changes at half the line frequency. To ensure that only the mean of the alternating signal of the phase comparator circuit affects the voltage-controlled oscillator, a low-pass filter is connected behind the phase comparator circuit. It has a long time constant so that the alternating signal produced by the alternating phase of the color synchronization signal is properly suppressed. This does mean, however, that changes in regulation are only compensated slowly.
In current video recorder systems during recording the band-limited brightness signal is frequency-modulated in a higher frequency range and the the color type signal is amplitude-modulated in a lower frequency range. At the same time, the color type signals of certain lines of a half-image are phase-shifted by a constant amount. During playback this phase shift is again cancelled on frequency conversion and thus, the phase of the components of the crosstalk interference brought about by the side tracks is changed. The cross-talk interference is suppressed in a peak filter. The output of the peak filter is connected to the input of the phase regulation circuit with the aid of which a carrier for the modulation is generated.
In a VHS system of the PAL or NTSC standard, the distance between the neighboring tracks is reduced when changing the tape from four to six or eight hours play. During playback of a four-hour tape, the cross-talk from neighboring tracks is so small that the input of the phase regulation circuit may be connected in front of the peak filter. This increases the rate of regulation of the phase regulation circuit. Without the use of the peak filter, there is considerable crosstalk on the playback of a six or eight-hour tape since the tracks are closer together than on a four-hour tape. Owing to the phase-shift during the frequency change in the control signal of the phase comparator circuit, this crosstalk interference occurs at a constant frequency which is lower than the line frequency, and is in a whole-number ratio to it. Besides the above interference through the PAL changeover in a PAL-VHS system, there is interference in the control signal of the phase comparator circuit caused by the phase shift of a quarter of the line frequency. In a VHS system of the NTSC standard, interference caused by the phase shift occurs in the phase comparator circuit control signal at half the line frequency.